Canadian carrier Rogers has its firmware schedule up and it shows that the Nexus 6P is expected to receive Android 8.0 Oreo on September 11.

Keep in mind that itís entirely possible the schedule is inaccurate. Itís entirely possible that we can see the 6P get Oreo before, or, or after the expected date. If you do find the OTA notification before the eleventh on the Nexus 6P, be sure to leave us a tip!

I have a Nexus 6P, just checked the updates menu in settings. It said there is no update. I refreshed and it said the same. I refreshed again just to be sure and there it is! It is downloading right now.